ATM multi-purpose buttons

Recently, my girlfriend and I stopped by her bank so she could make an ATM withdrawal. (Remember, it's my girlfriend. I don't routinely observe strangers' interactions with ATMs. This was a special opportunity for observation, for this reason.)

Like many ATM machines, in addition to a numeric keypad, there is a set of four or five physically unlabelled buttons arranged in a column along the right side of a small computer screen. These buttons do not always have a function. During certain steps in an ATM session, some or all of the buttons are assigned functions, and the display shows their labels on the right side of the screen, aligned with the buttons.

She entered a PIN on the keypad (No, I didn't observe that closely.) and pressed the multi-purpose buttons as she proceeded with the session, to choose a transaction, an account, a withdrawal amount, and whether she wanted a receipt. On this occasion, however, part way into the session, she cancelled her transaction and start over. She told me that she accidentally chose the wrong account.

When she reattempted the transaction, I noticed her stooping down slightly to look at the screen and multi-purpose buttons when she needed to use them, taking more time to ensure she was pressing the button corresponding to the account she wanted.

The source of ambiguity in the multi-purpose buttons' functions is not apparent until you stand directly in front of the ATM. As shown in the diagrams above, the screen is recessed deeper than the buttons and is covered by a plate of glass or plastic, presumably for protection, since it is far less expensive to replace the plate than a screen tube scratched from frequent use. If the user's height is such that, from their point of view, the buttons and screen line up, the mapping between on-screen labels and buttons is clear. However, if, as in the case of my girlfriend, the user's point of view is higher, the buttons appear shifted lower than the on-screen labels, and it is easy to press a button higher than the one you really want, particularly if only two or three of the buttons have functions.

Using multi-purpose buttons such as these seems more reasonable than having an alphanumeric keyboard or many more special function keys, which might result in a cluttered interface. It is also less expensive than using a touch-screen, which would eliminate the ambiguity described above but would require visual and/or auditory feedback to acknowledge button presses. Orienting them vertically also seems reasonable, since the on-screen labels would be difficult to read if their text had to be oriented vertically for a horizontal row of buttons instead. The problem is obviously the result of having the screen at a different depth than the buttons, making the user's angle of view a critical factor in proper interpretation of the on-screen labels.

some unanswered design questions:

• With so many different ATM locations, does the bank standardize the height at which the screen should be relative to the ground?
• Why is it necessary to recess the display so deeply?
• Did designers consider using only four buttons at the four corners of the display?